Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $44.44   6.803%   $47.4633   $47.46   $47.45   $47.50  
  Purchase #2 $158.92   9.363%   $173.7997   $173.80   $173.80   $173.80  
  Purchase #3 $127.99   6.577%   $136.4079   $136.41   $136.40   $136.40  
  Purchase #4 $139.45   9.272%   $152.3798   $152.38   $152.40   $152.40  
  Purchase #5 $71.87   3.198%   $74.1684   $74.17   $74.15   $74.20  
  Purchase #6 $246.63   4.788%   $258.4386   $258.44   $258.45   $258.40  
  Purchase #7 $117.77   4.446%   $123.0061   $123.01   $123.00   $123.00  
  7 purchase totals = $907.07       $965.6638   $965.67   $965.65   $965.70